Sera from tumor patients may contain antibodies reacting with their own tumor cells which may be detected using suitable sensitive serological assays such as the mixed hemadsorption assay (MHA). When the cells and the serum come from the same individual this is known as autologous reactivity; when the serum is tested on cells from a different individual then the reaction is known as an allogeneic reactivity. The analysis of the specificity of antibodies in an autologous reaction is easier than in an allogeneic reaction because reactions with unrelated allogeneic antibodies are eliminated. This approach to study tumor cells (autologous typing) has led to the detection of a number of antigens of melanoma and other tumors that have very restricted distributions.
One approach in the search for human tumor-associated antigens has been to test sera from tumor patients for reactivity against the autologous tumor cell line. A possible disadvantage of this approach is that antigens which elicit cellular immunity but not antibodies will not be detected. This point is significant since in animal models tumor-specific transplantation antigens, which elicit strong cell-mediated immunity, do not in general induce antibodies. Still if antibodies reacting with autologous tumor cells are found, they provide a reagent that can be tested for specificity with a thoroughness not readily attainable using assays for T cell immunity. Several interesting antibodies have been defined by this approach. Some of these unique antigens are found only on an individual tumor; they have been designated Class 1 antigens. A detailed biochemical characterization of these antigens has been difficult due to the fact that none could be detected by immunoprecipitation. Thus antibodies to the Class 1 antigen AU have been found in serum of patient AU (Carey, et al. Proc. Nat'l. Acad. Sci., U.S.A., 73:3278 (1976)), but characterization of the antigen has been difficult since the antibodies are non-precipitating. Accordingly, efforts have been exerted to locate precipitating autologous antibodies to tumors.